1. Field of the Invention
The invention relates generally to a gas circulation engine that has a combustion chamber and a circulation path that connects an intake-side portion and an exhaust-side portion of the combustion chamber to each other. More specifically, the invention relates to a working gas circulation engine that has a combustion chamber which is supplied with an oxidant, fuel, the combustion (oxidation) of which is promoted by the oxidant, and working gas that generates power with the use of combustion of the fuel, and a circulation path that connects an intake-side portion and an exhaust-side portion of the combustion chamber to each other, and that is formed in such a manner that the working gas is circulated back to the combustion chamber through the circulation path without being released into the atmosphere.
2. Description of the Related Art
Working gas circulation engines of this type are so-called closed-cycle engines, and described in, for example, Japanese Patent Application Publication No. 11-93681 (JP-A-11-93681) and Japanese Patent Application Publication No. 2007-247524 (JP-A-2007-247524). In the working gas circulation engines described in JP-A-11-93681 and JP-A-2007-247524, oxygen and hydrogen are supplied to a combustion chamber as an oxidant and fuel, respectively, and argon is circulated as working gas in order to enhance the thermal efficiency. In these working gas circulation engines, argon is thermally expanded due to the combustion of hydrogen that takes place in the combustion chamber. The thermal expansion of argon pushes a piston down so that power is produced. Because water vapor is generated due to the combustion of hydrogen that takes place in the combustion chamber, the water vapor is discharged into a circulation path along with the argon. Therefore, in the working gas circulation engines, a condenser that liquefies the water vapor to remove it is provided in the circulation path so that only argon, which is used as the working gas, is circulated back to the combustion chamber.
In the working gas circulation engines that are the closed-cycle engines, the fuel and the oxidant are stored in respective tanks at high pressures, and supplied from the tanks at high pressures. Therefore, after the engine is stopped, the fuel and the oxidant remain in respective supply paths at high pressures. Accordingly, the high-pressure fuel and the high-pressure oxidant may leak into the combustion chamber and the circulation path through, for example, a fuel injection device that injects the fuel, an oxidant supply device that supplies the oxidant, and a clearance between an intake valve and a cylinder head. If the fuel and the oxidant leak into, for example, the combustion chamber, the amount of fuel and the amount of oxidant in the combustion chamber exceed target supply amounts when the engine is restarted or after the engine is restarted. This may cause some inconveniences, for example, this hinders proper combustion of the fuel.